1. Field of the Invention
The present invention relates generally to vascular grafts having at least one flared end to facilitate anastomosis to a blood vessel, such as a vein or an artery, or between blood vessels. More particularly, the present invention relates to polymer grafts having at least one flared end, which forms a skirt or cuff to form an anastomosis with the aorta.
2. Description of Related Art
When a blood vessel becomes occluded, a vascular surgeon may restore proper blood flow by performing a surgical bypass procedure. In the medical treatment of patients with diseased arteries or veins, surgeons may replace or bypass the occluded vessel with prosthetic conduits, such as vascular grafts. Examples of such grafts have been made from a polyester fabric (e.g., Dacron(copyright) fabric), or polytetrofluroethylene (PTFE) fabric (e.g., Teflon(copyright) fabric). Fabrics woven or knitted of these polymers also have been used as patches or reinforcements. Known procedures for restoring proper blood flow include creation of a formal surgical incision and exposure of the blocked artery or vein. A prosthetic bypass graft or a natural vein then may be sutured to the occluded vessel both upstream and downstream of the occlusion in order to divert the flow of blood around the occlusion. Known grafts, however, may kink or collapse mechanically under a variety of circumstances, such as when the graft is bent during the contraction of the surrounding muscle or tissue, or when external pressure is applied to the graft when the graft recipient moves. In addition, small diameter vascular grafts, i.e., internal diameters less than about six (6) mm, have a tendency to become obstructed due to neointimal proliferation or thrombus formation.
A solution to these problems has consisted of the reinforcement of the walls of vascular grafts by the attachment of either discrete polymeric rings or of a continuous spiral of polymeric bands to a portion, albeit sometimes a small portion, of the exterior surface of the graft. A reinforcing member may be fixed over the graft component through a variety of means or methods. Such reinforcing members are described in U.S. Pat. No. 5,085,065, which is incorporated herein by reference. The means or methods chosen to accomplish the fixation affects to a certain degree the graft""s compliance, and the resultant compliance of the reinforced graft assembly may vary between applications of the reinforcing member. In addition, compliance is adjustable by winding the fibers of a reinforcing member at an angle, which may enhance kink resistance.
Although it may be desirable to reinforce grafts to prevent kinking or collapse, it is also essential that the graft remain compliant. Natural blood vessels are compliant and can expand both radially and longitudinally as blood is pumped through them. Reinforcing members, however, may reduce the radial compliance or the longitudinal compliance, or both, of an artificial grafts. A non-compliant graft may reduce the pulsatile flow through the graft, thereby compromising the ability of the graft to function naturally to correct an occlusion. In addition to the method described above, compliance may be adjusted by varying the durometer hardness of the fibers from which the reinforcing member is made and of the base material for the graft. Nevertheless, known manufactured vascular grafts may exhibit limited compliance.
Therefore, a need has arisen for a compliant, kink-resistant, and easy to handle vascular graft, such as coronary artery bypass graft (CABG). It is a feature of a graft according to the present invention that it has at least one flared end. Because the diameter of blood vessels may vary between patients, as well as within each patient, it is desirable to have a vascular graft, which has a diameter on one end larger than that on the other end. It is an advantage of this flared end configuration that it facilitates surgical attachment of the graft to an artery, such as the aorta. It is a further advantage of this flared end configuration that the effects of neointimal proliferation may be reduced or eliminated, especially in small diameter vascular grafts. It is another feature of a graft according to the present invention that it may be made from polymeric materials, for example, polyurethanes, such as polyether urethanes, polycarbonate urethanes, polyester urethanes, silicone polyether urethanes, silicone polycarbonate urethanes, or the like. It is yet another feature of a graft according to the present invention that the side walls of the graft may be reinforced. In particular, the graft may be reinforced by a multi-layered construction.
Moreover, a graft according to the invention may be substantially cylindrical or tubular to attain increased graft strength and resistance to tearing, especially at connection points with an occluded and a bypass vein or artery. It is an advantage of the use of these polymeric materials that graft may be flexible and kink-resistant.
In an embodiment of the present invention, a bypass graft, such as a CABG, comprises a tubular portion having an internal tubular diameter and a first end and a second end. The tubular portion has a central axis. A flared portion has an adjoining end, wherein the adjoining end of the flared portion is integrally formed on and is substantially concentric with the second end of the tubular portion. The flared portion also has a flared end, wherein the flared end has an internal flared end diameter, such that the internal flared end diameter is greater than the internal tubular diameter; whereby the flared portion comprises a circumferential skirt for surgical attachment of the graft to a patient""s blood vessel, i.e., a vein or an artery.
The present invention provides a graft having a first and a second end. The first end is flared around the central axis of the internal diameter of the graft to form a skirt having a substantially circular opening larger than the internal diameter, for surgical attachment of the first end to a blood vessel, such as the aorta. The skirt may alternatively be asymmetrically flared around the central axis of the graft forming a substantially elliptically shaped opening, The circular or elliptical opening of the skirt may have an axis which is parallel to the axis of the internal diameter of the graft or, alternatively, the axis of the skirt may be at an oblique or other angle to the axis of the internal diameter of the graft, so that it may be readily sutured at an acute angle. In either the circular or the elliptically (e.g., asymmetrically) flared configurations, the skirt is adjustable, trimmable, or foldable to be readily adapted for suturing at an acute angle to a vein or an artery, such as the aorta.
Methods for forming multi-layered, polyurethane, CABG are also provided by coating suitably shaped mandrels with polyurethane materials. In a further embodiment of this invention, a method for manufacturing a bypass graft, comprises the steps of providing a mandrel having a tubular portion and a flared end with a flared end central axis; forming at least one layer of polyurethane over the mandrel; drying the at least one layer of polyurethane on the mandrel; forming a skirt edge around the flared end of the mandrel to form an opening at a predetermined angle to the flared end central axis; forming a second edge around the tubular portion of the mandrel; and removing the graft from the mandrel.
Other objects, features, and advantages will be apparent to those skilled in the art in view of the following detailed description of the drawings and the accompanying drawings.